This invention relates to energy absorbers, or attenuators, and in particular to energy attenuators which can be used to control the tensile or compressive forces within a structure.
It is frequently desirable to design a rigid structure in such a manner that when it is subjected to high tensile or compressive loads it fails gracefully. This "graceful degradation" feature is particularly applicable to situations where the structure comprises a conveyance, such as an automobile, railway car, or airplane, which may be subjected to high loads in the event of an accident. To be effective, these mechanisms must yield when specified forces are applied to them, and should be impervious to the evironment usually encountered in such conveyances--such as a high vibration level, weather, etc. In many situations, and particularly where a rebound force may be encountered, it is important that the attenuator be able to attenuate both tensile and compressive loads.
A variety of mechanisms have been employed as energy attenuators in the prior art. Some of these, such as the shear bolts employed in railway coupling mechanisms, are relatively inexpensive, and impervious to weather, and can be designed to yield at a design load, but they do not provide a continuous "stroking" force.
Those mechanisms which were designed to provide a stroking action, such as hydraulic shock absorbers; inertia reels, and even wire-bending attenuators, were usually expensive, and complicated. Further, the prior art attenuators were not dependable, and were particularly susceptible to the effects of weather, aging, and vibration. The prior art attenuators often did not stroke when the design load was applied, but instead yielded over a wide range of forces. This undesirably wide variation persisted in spite of tedious and expensive manufacturing methods. Most prior art attenuators were designed to respond to tensile or compressive loads, but not both.